[vtkusers] Problem when using vtkDistanceWidget in MFC

[Huoling Luo]

Hello vtk users,
I use vtkDistanceWidget combining with MFC to process distance measurement, and I encountered a strange problem.
vtkImageViewer2 is used to display an image, which is a data member of CVtkView (CVtkView is derived from CView). vtkRenderWindow and vtkRenderWindowInteractor are also the data members of CVtkView. I wrote a new class named DistanceWidgetObserver, the code is:
// DistanceWidgetObserver.hclass DistanceWidgetObserver : public vtkCommand {public:	DistanceWidgetObserver(vtkImageViewer2* pViewer,		vtkDistanceWidget* pDistanceWidget);	static DistanceWidgetObserver* New(vtkImageViewer2* pViewer,		vtkDistanceWidget* pDistanceWidget) 	{ 		return new DistanceWidgetObserver(pViewer, pDistanceWidget); 	}
protected:	~DistanceWidgetObserver();
	vtkImageViewer2* m_pViewer;	vtkDistanceWidget* m_pDistanceWidget;	vtkDistanceRepresentation2D* m_pDistanceRep;	vtkPointHandleRepresentation2D* m_pPointHandleRep;
private:	void Execute(vtkObject *caller, unsigned long, void*);};
// DistanceWidgetObserver.cppDistanceWidgetObserver::DistanceWidgetObserver(vtkImageViewer2* pViewer,												 vtkDistanceWidget* pDistanceWidget){    m_pViewer = pViewer;    m_pDistanceWidget = pDistanceWidget;    m_pDistanceRep = vtkDistanceRepresentation2D::New();    m_pPointHandleRep = vtkPointHandleRepresentation2D::New();}
DistanceWidgetObserver::~DistanceWidgetObserver(){...}
void DistanceWidgetObserver::Execute(vtkObject *caller,                                       unsigned long ulCommand,                                       void*) {    m_pDistanceWidget->SetInteractor(m_pViewer->GetRenderWindow()->GetInteractor());	m_pDistanceWidget->CreateDefaultRepresentation();
	m_pPointHandleRep->GetProperty()->SetColor(1,0,0);	m_pDistanceRep->SetHandleRepresentation(m_pPointHandleRep);
	m_pDistanceRep->GetAxis()->SetNumberOfMinorTicks(4);	m_pDistanceRep->GetAxis()->SetTickLength(5); 	m_pDistanceRep->GetAxis()->SetTitlePosition(0.5);	m_pDistanceRep->RulerModeOn();       	m_pDistanceRep->SetRulerDistance(10);
	m_pDistanceWidget->SetRepresentation(m_pDistanceRep);    	static_cast<vtkDistanceRepresentation *>(m_pDistanceWidget->GetRepresentation())		->SetLabelFormat("%-#.2f mm");}
Then I use DistanceWidgetObserver to instantiate a member in CVtkView, And in the function OnDraw() I wrote the following code:
// OnDraw() code:void CVtkView::OnDraw(){    ...    m_pDistanceObserver = DistanceWidgetObserver::New(m_pImageViewer, m_pDistanceWidget);    m_pImageViewer->Render();}
When I run this program and clicked the image, the program crashed.
Anyone knows why is it? If I did wrong, please correct me. Or please give me some tips on this topic of using vtkDistanceWidget combined with MFC. 
Regards & thank you
Huoling 		 	   		  
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